DE102022109740A1 - Method and device for carrying out optical coherence measurements for monitoring a machining process of a workpiece - Google Patents

Abstract

The invention relates to a method for carrying out optical coherence measurements for monitoring a machining process of a workpiece (12). The method comprises generating several high-energy processing beams and/or processing beam parts (18), which can be directed simultaneously at several impact points (22) according to a predetermined spot pattern (20) in order to carry out multispot processing of the workpiece (12), in which the spot pattern (20) is moved relative to the workpiece (12). The method further comprises generating a measuring beam (26) by means of an optical coherence tomograph (24), which can be directed selectively to different measuring positions (28). The method also includes defining a spot pattern (20) that defines at least two different impact points (22). The method further comprises defining a coordinate system (30), wherein the coordinate system (30) is stationary with respect to the spot pattern (20). The method also includes setting a measuring position (28) with respect to the coordinate system (30) during multispot processing.

Description

The invention relates to a method and a device for carrying out optical coherence measurements for monitoring a machining process of a workpiece.

High-energy processing beams such as laser beams are sometimes used to process workpieces. These are specifically aimed at one or more workpieces in order to carry out machining processes, for example laser beam welding. In the area where the high-energy processing beam hits the workpiece, a process zone is formed in which the material of the workpiece is melted. A so-called keyhole can form. This is located within a melt pool and is formed by a vapor capillary, which is created by the action of the processing jet on the workpiece.

Optical coherence measurements can be carried out to characterize workpieces and monitor machining processes. In such cases, machining systems often include an optical coherence tomograph that generates a measuring beam that can be directed onto the workpiece to carry out measurements in front of, behind and/or within the keyhole. A proven structure involves coupling the measuring beam into the processing beam and guiding the measuring beam and the processing beam essentially coaxially onto the workpiece via a common optics. A measuring scanner can be used here, for example in the form of an adjustable mirror arrangement, by means of which the measuring beam can be specifically shifted in two spatial directions.

In order to determine a penetration depth of the processing beam into the material of the workpiece, in other words to measure a welding depth, the measuring beam can be directed into the keyhole. The penetration depth provides valuable information about whether selected process parameters need to be adjusted and whether machining runs smoothly or whether, for example, the workpiece is completely penetrated accidentally. To prepare for such penetration depth measurements, it is common practice to first align the measuring beam and the processing beam congruently with one another. The alignment required for this is usually carried out by making a test shot with the processing beam on a sheet of metal, a piece of aluminum foil or another test workpiece. Like for example in DE 10 2017 213 511 A1 or DE 10 2015 012565 B3 As described, cameras can also be used to detect the beam position. The aim of such an alignment is to adjust the origin of the coordinate system, which is used to determine a measuring beam position or for the measuring scanner, to the processing point. The use of such a coordinate system is particularly useful when machining takes place along a machining path with a feed speed and, if necessary, with changes in direction. Due to the feed, the keyhole can form behind a current point of impact of the processing beam, which is why the measuring beam is positioned trailing. The use of a coordinate system to set a trailing measurement position allows direction-independent measurements of the penetration depth to be carried out. If the measuring beam position were to remain unchanged, the measured penetration depth would possibly depend on the feed direction and the feed speed, since the measuring beam might not reliably hit the keyhole.

For some processing operations, it has proven to be advantageous to use several focus points within the process zones, i.e. to direct processing beams or partial beams to several impact points at the same time. In such cases we also speak of so-called multispot processing. For example, optical fibers with multiple cores are known for generating multispots. Diffractive optical elements (DOEs) or prisms are often used to split a source beam into several processing beams. An example is given in this regard WO 2019/197423 A1 referred. The use of a multispot processing beam can be used, for example, to preheat the processed material, to burn off a zinc layer, to break up an oxide layer and/or to widen or enlarge the spot.

Based on the prior art, the invention is based on the object of being able to monitor multispot processing with high accuracy.

This task is solved by a method with the features of claim 1 and a device with the features of claim 10. Further developments can be found in the dependent claims.

A trailing positioning of an OCT measuring beam during multispot processing has not yet been considered. The inventors have recognized that the common procedure of a test shot to determine a processing beam position for multispot processing provides several test shot holes, but this test shot pattern cannot be equated with that Presence of multiple keyholes during machining, especially in the case of feed. The inventors have also recognized that directing the measuring beam at the position of one of the test shot holes would under certain circumstances not allow direction-independent penetration depth measurement during processing. According to the invention, it is proposed to define a coordinate system for setting a measurement position in a suitable manner depending on a spot pattern.

The invention relates to a method for carrying out optical coherence measurements for monitoring a machining process of a workpiece. The method includes generating a plurality of high-energy processing beams and/or processing beam parts, which can be directed simultaneously at several impact points according to a predetermined spot pattern in order to carry out multispot processing of the workpiece, in which the spot pattern is moved relative to the workpiece. The method also includes generating a measuring beam using an optical coherence tomograph, which can optionally be directed to different measuring positions. The method also includes setting a spot pattern that defines at least two different impact points. The method further includes determining a coordinate system, wherein the coordinate system is stationary with respect to the spot pattern. The method also includes setting a measurement position with respect to the coordinate system during multispot processing.

The invention also relates to a device for machining a workpiece and for carrying out optical coherence measurements for monitoring a machining process of the workpiece, in particular according to a method according to the invention. The device comprises a processing unit with a processing beam source for generating a plurality of high-energy processing beams and/or processing beam parts, which can be directed simultaneously at several impact points according to a predetermined spot pattern in order to carry out multispot processing of the workpiece, in which the spot pattern is moved relative to the workpiece. Furthermore, the device comprises an optical coherence tomograph for generating a measuring beam, which can be directed selectively to different measuring positions. The device also includes a control unit that is set up to set a spot pattern that defines at least two different impact points, set a coordinate system, the coordinate system being stationary with respect to the spot pattern, and setting a measurement position with respect to the coordinate system during multispot processing.

The method according to the invention and the device according to the invention enable multispot processing to be monitored with high accuracy. Thanks to the features according to the invention, an OCT system can be usefully used to measure penetration depths in multispot processing. Even when machining with a feed and even for complicated machining paths, precise, direction-independent measurement can be carried out. In particular, during multispot processing, a measuring beam can be positioned specifically and reliably in such a way that it hits a keyhole formed by the processing beam, for almost any processing path and, if necessary, variable processing directions and variable feed speeds.

The at least one processing beam can be a processing laser beam. The processing beam source can be a processing laser. The device can include a processing head, which can be mounted on an industrial robot, for example. The machining head can be movable relative to the workpiece, wherein the relative movement can be generated by moving the machining head and/or by moving the workpiece. In some embodiments, a single processing beam may be generated that is divided into multiple processing beams and/or processing beam parts. At least one DOE, at least one prism and/or at least one optical fiber with multiple cores can be used for this. If reference is made below to a processing beam or to the processing beam, this should be understood to mean that it can be both a beam of several processing beams and, alternatively or additionally, a single processing beam that is divided along its beam path. This can in particular mean the processing beam both before and after its division. Regardless of this, a spot pattern with several spots is available for processing.

A processing scanner can be provided, by means of which the processing beam can be displaced relative to the workpiece. The machining scanner can allow a machining position on the workpiece to be shifted in one or two spatial directions. For example, the processing scanner can have at least one and in particular two movable mirrors, by means of which the processing beam can be shifted in a targeted manner.

The measuring beam can be coupled into the processing beam and/or into the processing beam optics. A measuring scanner can be provided be hen, by means of which the measuring beam can be displaced relative to the processing beam or relative to the spot pattern. The measuring beam is in particular a single beam. In addition to the measuring scanner, the measuring beam can also be moved via the processing scanner. In this configuration, for example, the processing beam is guided over the processing scanner but not over the measuring scanner and the measuring beam is guided over both the measuring scanner and the processing scanner. The measuring beam can therefore be displaced relative to the spot pattern by means of the measuring scanner, even if the processing scanner is moved.

The optical coherence tomograph can include a measuring arm in which the measuring beam is optically guided. Furthermore, the optical coherence tomograph can include a reference arm in which a reference beam is optically guided. The measuring beam and reference beam can be generated from a source beam, in particular a broadband, short-coherent light beam, using a beam splitter. The measuring beam and the reference beam can be brought into interference in a generally known manner in order to carry out optical coherence measurements.

It is understood that the spot pattern includes at least two spots, for example two or three or four or five or an even larger number of individual spots. The spot pattern can be selected so that a single weld seam or a single processing track is formed during multispot processing. In this respect, the spot pattern can be different from an arrangement of several unconnected processing positions at different locations on the workpiece. In some embodiments, the processing beam or the processing beams and/or processing beam parts are guided onto the workpiece via a common processing beam optics and/or via a common processing scanner. The spot pattern can thereby be moved as a whole relative to the workpiece. At different processing positions that can be set using the processing scanner, an at least essentially unchanged spot pattern hits the workpiece, at least as long as the spot pattern as such is not changed or adjusted.

Setting the spot pattern can include setting at least one optical element that serves to split the processing beam. As mentioned, this optical element can be at least one DOE, at least one prism and/or at least one optical fiber with multiple cores. The spot pattern can be adjustable and/or preset and/or preset by a user. In some embodiments, the spot pattern can be set automatically.

Setting the coordinate system may include setting an origin and/or setting at least two axes. The coordinate system can be a two-dimensional, in particular orthogonal, coordinate system. Its axes can, for example, run essentially parallel to a processing plane. During machining, a surface section of the workpiece to be machined can be arranged parallel to and/or in the machining plane. The coordinate system can be stationary with respect to the spot pattern in such a way that its origin has a defined and/or constant distance from the individual spots of the spot pattern. Furthermore, the coordinate system can be stationary in the sense that the orientation of the axes of the coordinate system does not change relative to the spot pattern. In other words, the coordinate system can be movable and/or rotatable with the spot pattern.

Processing takes place in particular along a processing path. In other words, during machining, the machining beam is displaced along the machining path relative to the workpiece. This can have any course and may have straight, curved, angled, arcuate or other sections. The machining path may be defined in terms of a machining coordinate system. The machining coordinate system can be, for example, a reference system of the device and/or a reference system for the workpiece. The machining coordinate system can be stationary to the workpiece, so that the machining path is defined relative to the workpiece. The coordinate system for the measuring position can therefore be moved and/or accelerated relative to the processing coordinate system, in particular both translationally and rotationally. The processing coordinate system can be a two-dimensional, in particular orthogonal, coordinate system. The axes of the machining coordinate system and the axes of the coordinate system for the measuring position can lie in a common plane regardless of a movement and/or acceleration state of the coordinate system for the measuring position.

Setting the measurement position with respect to the coordinate system during multispot processing may include expressing the measurement position in the coordinates of the coordinate system. A measuring position that is constant with respect to the coordinate system is therefore relative to the machining tung coordinate system moves and / or accelerates depending on the processing path.

In some embodiments of the invention, an origin of the coordinate system is positioned at a center of the spot pattern and/or between the spots of the spot pattern. If the spot pattern is known, for example by specification and/or by a test measurement, the origin can be easily determined based on the spot pattern and following a reliable rule. If a test measurement is carried out in which the spot pattern is directed at a test workpiece as part of a test shot, an area that has been processed for a test can, for example, be measured using the measuring beam, for example by scanning.

A particularly useful embodiment, which also allows intuitive tracking of a set tracking of the measuring position and/or simple programming, can be achieved in particular if a center of gravity of the spot pattern is chosen as the origin of the coordinate system. The center of gravity can be a geometric center of gravity and/or a center of gravity weighted according to intensity and/or power at the impact points of the spot pattern. The intensities and/or the power at the impact points can be determined based on a test measurement and/or based on a specification and/or based on an estimate. An area that has been processed as part of a test measurement can, for example, be examined for a depth and/or a diameter of the individual shot holes created as a test, from which conclusions can be drawn about the intensities and/or the power at the individual impact points.

In some embodiments, the measurement position may differ from each point of impact of the spot pattern. The inventors have found that in many cases the keyhole forms in a location that is different from all spots, which is why this choice of measuring position can have the advantage that a penetration depth can be precisely determined because the measuring beam is in the process during processing Keyhole is directed. It should be noted that the measuring position can depend on the current machining situation. In particular, a suitable overrun can depend on a direction and/or a feed rate. In this regard, the inventors have found that even for significantly different processing positions, the keyhole regularly forms at a position that does not correspond to any of the impact points, even if the position of the keyhole is changeable.

With multispot editing, a single keyhole can be formed. The measuring position can be directed into the keyhole during multispot processing. In this way, the advantages of multispot processing can be combined with the advantages of precise penetration depth measurement.

The method may further include performing a machining in which the spot pattern is moved relative to the workpiece at a feed speed and/or in a machining direction. In addition, the method can include adjusting the measuring position depending on an amount of the feed speed and/or an orientation of the processing direction with respect to the coordinate system. In particular, the tracking of the measuring position is set depending on and/or proportional to the feed speed, i.e. H. the higher the feed speed, the greater the overtravel is set. Taking the orientation into account can take into account the fact that the keyhole position or the distance of the keyhole from the origin of the coordinate system can depend on the orientation, in particular the relative rotation, of the spot pattern in relation to the processing direction or the processing coordinate system. Melt pool and keyhole can form differently depending on the orientation of the spot pattern, for example based on their position and/or geometry.

Furthermore, the method can include carrying out a test processing of a test workpiece, in which the spot pattern is moved with at least one feed speed in at least two different processing directions. In addition, the method can include shifting the measuring position with respect to the coordinate system during test processing, in particular along at least one line parallel and/or perpendicular and/or oblique to a current processing direction, in order to obtain measurement data from which a profile of a penetration depth into the test workpiece can be determined is. Furthermore, the method can include determining a dependence of the setting of the measuring position on an orientation of the machining direction and the feed rate with respect to the coordinate system. In this way, a penetration depth measurement can also be determined reliably and precisely for changing machining directions by using the test machining to determine how different feed speeds and/or different machining directions affect the position of the keyhole. This information can then be used to set the measuring position appropriately.

The test processing may include moving the spot pattern at several different feed rates. Several different machining directions can then be used as a test for each feed speed. In other words, during test processing, the spot pattern can be moved for the at least two different processing directions, each with at least two different feed directions. This provides a more complete picture of the dependence of the keyhole position on the selected machining path and the selected feed along the machining path. According to the information received, the measuring position can be adjusted automatically on the basis of a predetermined movement plan, for example a predetermined combination of processing path and, if necessary, variable feed speed.

It is particularly pointed out that all features and properties described in relation to devices, but also procedures, can be transferred to methods according to the invention and can be used in the sense of the invention and are considered to be disclosed. The same applies in the opposite direction. This means that structural features mentioned in relation to methods, i.e. features corresponding to the device, can also be taken into account, claimed and also included in the disclosure within the scope of the device claims.

The present invention is described below by way of example using the attached figures. The drawing, description and claims contain numerous features in combination. The person skilled in the art will also expediently consider the features individually and use them in combination within the scope of the claims.

• 1 eine schematische Darstellung einer Vorrichtung zur Bearbeitung eines Werkstücks und zur Durchführung optischer Kohärenztomographiemessungen für eine Überwachung eines Bearbeitungsprozesses;
• 2 eine schematische Darstellung eines Spotmusters für eine Multispot-Bearbeitung;
• 3 eine schematische Darstellung eines Abschnitts eines Bearbeitungspfads;
• 4 eine schematische Darstellung einer Ausbildung eines Keyholes bei einer Testbearbeitung mit einer ersten Bearbeitungsrichtung;
• 5 eine schematische Darstellung einer Ausbildung eines Keyholes bei einer Testbearbeitung mit einer zweiten Bearbeitungsrichtung;
• 6 eine schematische Veranschaulichung einer Abhängigkeit einer Keyholeposition von einer Bearbeitungsrichtung; und
• 7 ein schematisches Ablaufdiagramm eines Verfahrens zur Bearbeitung eines Werkstücks und zur Durchführung optischer Kohärenztomographiemessungen für eine Überwachung eines Bearbeitungsprozesses.

Show it:

• 1 a schematic representation of a device for machining a workpiece and for carrying out optical coherence tomography measurements for monitoring a machining process;
• 2 a schematic representation of a spot pattern for multispot processing;
• 3 a schematic representation of a portion of an editing path;
• 4 a schematic representation of a formation of a keyhole during a test machining with a first machining direction;
• 5 a schematic representation of the formation of a keyhole during test machining with a second machining direction;
• 6 a schematic illustration of a dependence of a keyhole position on a machining direction; and
• 7 a schematic flowchart of a method for machining a workpiece and for carrying out optical coherence tomography measurements for monitoring a machining process.

1 shows a schematic representation of a device 10 for machining a workpiece 12 and for carrying out optical coherence measurements for monitoring a machining process. The workpiece 12 can be, for example, a sheet metal part or another component made of metal, as well as a combination of several parts that are to be connected, in particular welded, for example during processing. The device 10 includes a processing unit 14, which includes a processing beam source 16, which generates a high-energy processing beam 18. In the case shown, the processing beam source 16 comprises a laser that generates a processing laser beam. The processing unit 14 can have an adjustable collimation lens 32.

In the example shown, the processing unit 14 includes a processing head 34. The processing beam 18 can be coupled into the processing head 34 via an interface 36 of the processing head 34. The processing beam 18 can be guided to the processing head 34, for example, through an optical fiber. In the case shown, the processing head 34 is arranged on an industrial robot, not shown, by means of which the processing head 34 can be moved relative to the workpiece 12. In other embodiments, the workpiece 12 may alternatively or additionally be movable.

The device 10 also includes an optical coherence tomograph 24 with an OCT measuring device 38, which is connected to a measuring arm 42 and a reference arm 44 via a beam splitter 40.

The OCT measuring device 38 is designed with a measuring beam source 46 for generating a measuring beam 26 and a spectrometer 48 for detecting a superimposed measuring radiation. Furthermore, the OCT measuring device 38 can include a circulator 50, which connects the beam splitter 40 via a fiber or a light guide 52 to the measuring beam source 46 or the spectrometer 48, depending on the direction of travel of the incoming light.

The measuring arm 42 of the optical coherence tomograph 24 extends to the workpiece 12. The measuring arm 42 can have an adjustable collimation tion lens 54 include. Furthermore, an interface 38 can be provided, via which the measuring beam 26 is coupled into the processing head 34.

The device 10 includes a measuring scanner 56. In the illustrated embodiment, the measuring scanner 56 includes two movable mirrors that can be pivoted in two different spatial directions. This allows the measuring beam 26 to be shifted in a targeted manner.

The device 10 further comprises a processing scanner 58. In the case shown, the processing scanner 58 is part of the processing unit 14. The processing scanner 58 allows the processing beam 18 to be displaced in two spatial directions. The processing scanner 58 expediently comprises two mirrors arranged one behind the other along the optical path of the processing beam 18, each of which can be pivoted in a spatial direction. By moving both mirrors, the processing beam 18 can be shifted in one plane. By means of the processing scanner 58, the processing beam 18 can be moved so that an impact point on the workpiece 12 can be changed.

The processing unit 14 includes a partially transparent mirror 60. This directs the processing beam 18 onto the processing scanner 58. In addition, the measuring beam 26 passes through the partially transparent mirror 60 and also hits the processing scanner 58. The measuring beam 26 can thus be coupled into the processing beam 18. The measuring beam 26 and the processing beam 18 can be moved together by means of the processing scanner 18. Since the measuring beam 26 can also be displaced by means of the measuring scanner 56, the point of impact of the measuring beam 26 on the workpiece 12, i.e. a measuring position 28, can be displaced relative to the point of impact of the processing beam 18 and independently of the processing beam 18 on the workpiece 12. This makes measurements possible both at a current processing position and at different measuring positions 28. In particular, different measuring positions 28 can be set, for example along measuring lines or at certain individual points.

The device 10 also has focusing optics 62. The focusing optics 62 may, in some cases, include an F-theta lens located behind the processing scanner 58. Alternatively or additionally, pre-focus optics can be provided, for example directly in front of the processing scanner 58. The processing beam 18 and the measuring beam 26 both pass through the focusing optics 62.

From this it can be seen that the measuring arm 42 extends from the beam splitter 40 to the point of impact of the measuring beam 26 on the workpiece 12. The reference arm 44 is adapted to the measuring arm 42 in terms of its optical properties, in particular with regard to its optical path and/or its dispersion. In this way, distance values can be determined using OCT in a known manner by superimposing the light that runs in the measuring arm 42 or in the reference arm 44.

The processing system 10 has a control unit 64. The control unit 64 can be a central control unit that controls both the processing unit 14 and the optical coherence tomograph 24. Alternatively or additionally, separate and/or separate control units can be provided. The control unit 64 or control units include at least one processor and a memory for temporary and/or permanent storage of raw data, preprocessed data, evaluated data, program code and the like. The functions of the control unit 64 will be discussed again below. It is understood that the mentioned functions of the device 10 and its components as well as the mentioned methods are carried out by the control unit 64. Furthermore, a computer program product, not shown, is provided which includes instructions that can be executed by the control unit in order to carry out the control functions mentioned. The computer program product can include a particularly non-volatile storage medium on which the instructions are stored.

The processing unit 14 is set up to carry out multispot processing. For this purpose, the processing beam 18 is divided into several processing beams or processing beam parts, which can be directed together in a specific spot pattern 20 onto the workpiece 12. This defines several impact points 22. In the case shown as an example, an optical element 66 is provided, by means of which the spot pattern 20 can be generated by suitably dividing the processing beam 18. This can be, for example, one or more birefringent beam splitter elements, prisms, DOEs, multi-core fibers or suitable combinations thereof.

The spot pattern 20 can be adjustable. In particular, relative positions of the impact points 22, a number of impact points 22 and/or a relative power or intensity of the individual impact points can be adjustable. The spot pattern 20 is more precise 2 shown. To illustrate this, a simple spot pattern is 20 with four impact points 22 selected, which are arranged in a square or a diamond. However, it goes without saying that other spot patterns and also a different number of impact points can be used. For example, the spot pattern 20 can include two impact points 22, which are arranged at a certain distance from one another, or three impact points 22, which are located at corners of a, in particular isosceles, triangle. Spot patterns 20 with an irregular polygonal arrangement of impact points 22 can also be used.

With reference to 3 During multispot machining of the workpiece 12, the processing beam 18 generates a keyhole 68, which is formed within a melt pool. 3 schematically represents the situation for a top view of a machined area of the workpiece 12. The impact points 22 of the spot pattern 20 are arranged at short distances from one another, for example in the range of millimeters or centimeters. A single keyhole is formed during processing, or in other words a single keyhole.

In 3 It can also be seen that during processing, a feed in a processing direction 70 can take place. This is predetermined by a processing path 72, along which processing takes place at a specific, optionally variable feed speed. Due to the feed, the keyhole 68 forms with a certain overtravel in relation to the machining direction. In order to be able to monitor the machining process as accurately as possible, the measuring beam 26 is directed into the keyhole 68. This allows the penetration depth of the processing beam 18 to be precisely determined, which in turn can be used to set and/or regulate process parameters appropriately.

As in 3 is also shown, a distance 74 from the spot pattern 20 can depend on the processing direction 70. In 3 This distance is illustrated relative to a point in the center of the spot pattern, which is marked by a cross. This dependency comes about because the spot pattern 20 rotates relative to the processing direction 70 during processing along the processing path 72. The energy input into the material in relation to the processing direction depends on the orientation of the spot pattern 20 because feed occurs in a specific direction. This is based on the two situations on the left and right side of 3 illustrated. In addition, there is a dependency on the feed speed in such a way that the distances 74 are correspondingly larger for higher feed speeds.

In order to reliably direct the measuring beam 26 into the keyhole 68 in different processing situations, the control unit 64 is set up to define a coordinate system 30 that is stationary with respect to the spot pattern 20. The measuring position 28 is then relative to the coordinate system 30 (cf. 2 and 3 ) set. For example, the tracking of the measuring position 28 is set based on the coordinate system 30. The measuring position 28 is expediently set in such a way that it lies within the keyhole 68 in every processing situation. The measuring position 28 is thus set depending on the processing direction 70 and the feed speed.

A machining coordinate system 76 can be used, with respect to which the machining path 72 is defined. The machining coordinate system 76 can be stationary relative to the workpiece 12, for example. The coordinate system 30 thus rotates during processing along the processing path 72 relative to the processing coordinate system 76, as does the spot pattern 20.

In the case shown as an example, the origin of the coordinate system 30 is positioned in the center of the spot pattern 20. The illustrated axes of the coordinate system 30 only show the axis directions as an example, but do not mark the origin. In the present case, the origin is placed on the geometric center of gravity of the spot pattern 20, i.e. it is located where the cross is drawn. To determine the origin, a test shot can be carried out on a test workpiece, from which the individual impact points 22 can be identified. These can be detected optically or can also be found using scanning through the measuring beam 28. Based on this, the geometric center of gravity can be determined.

In some embodiments, the origin can also be placed in a center of gravity weighted according to the respective intensity at the impact points 22 and/or the respective power at the impact points 22. The origin can then be closer to those impact points 22 where there is a lot of power.

Due to the mentioned dependence of the overtravel of the keyhole 68 on the processing direction 70 and the feed rate, a calibration measurement may be appropriate. For this purpose, a test processing of a test workpiece is carried out, in which the spot pattern 20 is moved in different processing directions 70. This is exemplified in the 4 and 5 shown. In addition, different feed speeds can be used. The Keyhole 68 then occurs at a different location depending on the respective processing direction 70 and, if applicable, feed direction.

To find the keyhole, a measurement is carried out using the measuring beam 26 during the test processing. For this purpose, the measuring beam 26 is displaced, for example, along a line 78, and an associated height profile is measured. This height profile shows how far the measuring beam 26 penetrates into the workpiece 12 at the respective measuring position 28, so it is a penetration depth profile. Such a measuring line includes several measuring positions 28, onto which the measuring beam 26 is specifically directed. The position of the keyhole can then be determined from the height profile, for example by determining a position of maximum depth. In the case shown as an example, a measuring line is selected parallel to the feed direction 70, which runs through the origin of the coordinate system 30. Additionally or alternatively, measuring lines or other measuring position distributions can be used, such as measuring lines transverse or oblique to the processing direction and/or measuring lines that are laterally offset with respect to the origin and/or the feed direction.

The keyhole positions obtained in this way are used to determine a dependence of the setting of the measuring position 28 on the orientation of the processing direction 70 and the feed speed with respect to the coordinate system 30. The dependency is stored in the control unit 64, so that a suitable measuring position 28 for penetration depth measurements can always be set depending on the processing situation. This takes into account the direction- and feed-dependent overtravel.

6 illustrates this dependency. The dashed arrows symbolize the respective processing direction. The spot pattern 20 is shown in the center. Solid line 80 marks a first set of keyhole positions found for a first feed rate. The directionality is clearly visible. The dotted line 82 marks a second set of keyhole positions determined for a second feed rate that is greater than the first feed rate. There is also a directional dependency here.

The above statements also relate to a method for machining a workpiece 12 and for carrying out optical coherence measurements for monitoring a machining process of the workpiece 12. The method is carried out, for example, with the device 10 described. A schematic flowchart of such a process is in the 7 shown.

In a step S1, several high-energy processing beams and/or processing beam parts 18 are generated, which can be directed simultaneously at several impact points 22 according to a predetermined spot pattern 20 in order to carry out multispot processing of the workpiece 12, in which the spot pattern 20 moves relative to the workpiece 12 becomes.

In a step S2, a measuring beam 26 is generated by means of an optical coherence tomograph 24, which can be directed selectively to different measuring positions 28.

In a step S3, a spot pattern 20 is defined, which defines at least two different impact points 22.

In a step S4, a coordinate system 30 is determined, the coordinate system 30 being stationary with respect to the spot pattern 20.

In a step S5, a measuring position 28 is set with respect to the coordinate system 30 during multispot processing.

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102017213511 A1 [0004]
• DE 102015012565 B3 [0004]
• WO 2019/197423 A1 [0005]

Claims (10)

Method for carrying out optical coherence measurements for monitoring a machining process of a workpiece (12), comprising: Generating several high-energy processing beams and/or processing beam parts (18), which can be directed simultaneously at several impact points (22) according to a predetermined spot pattern (20) in order to carry out multispot processing of the workpiece (12), in which the spot pattern (20) is relative is moved to the workpiece (12); Generating a measuring beam (26) by means of an optical coherence tomograph (24), which can be directed selectively to different measuring positions (28); defining a spot pattern (20) that defines at least two different impact points (22); Determining a coordinate system (30), the coordinate system (30) being stationary with respect to the spot pattern (20); and Setting a measuring position (28) with respect to the coordinate system (30) during multispot processing. Procedure according to Claim 1 , wherein an origin of the coordinate system (30) is positioned in a center of the spot pattern (20). Procedure according to Claim 1 or 2 , whereby a center of gravity of the spot pattern (20) is selected as the origin of the coordinate system (30). Procedure according to Claim 3 , wherein the center of gravity is a geometric center of gravity and/or a center of gravity weighted according to intensity and/or power at the impact points (22) of the spot pattern (20). Method according to one of the preceding claims, wherein the measuring position (28) differs from each impact point (22) of the spot pattern (20). Method according to one of the preceding claims, wherein a single keyhole (68) is formed during multispot processing, and whereby the measuring position is directed into the keyhole (68) during multispot processing. Method according to one of the preceding claims, further comprising: Carrying out a machining in which the spot pattern (20) is moved relative to the workpiece (12) at a feed speed and/or in a machining direction (70); and Setting the measuring position (28) depending on an amount of the feed speed and/or an orientation of the processing direction (70) with respect to the coordinate system (30). Procedure according to Claim 7 , further comprising: carrying out a test processing of a test workpiece, in which the spot pattern (20) is moved with at least one feed speed in at least two different processing directions (70); Displacing the measuring position (28) with respect to the coordinate system (30) during test processing, in particular along at least one line (78) parallel and/or perpendicular and/or oblique to a current processing direction (70), in order to obtain measurement data from which a profile a penetration depth into the test workpiece can be determined; and determining a dependence of the setting of the measuring position (28) on an orientation of the processing direction (70) and the feed rate with respect to the coordinate system (30). Procedure according to Claim 8 , wherein during the test processing the spot pattern (20) is moved for the at least two different processing directions (70), each with at least two different feed directions. Device (10) for machining a workpiece (12) and for carrying out optical coherence measurements for monitoring a machining process of the workpiece (12), in particular according to a method according to one of the preceding claims, wherein the device comprises: a machining unit (14) with a machining beam source (16) for generating several high-energy processing beams and/or processing beam parts (18), which can be directed simultaneously at several impact points (22) according to a predetermined spot pattern (20) in order to carry out multispot processing of the workpiece (12), in which the spot pattern (20) is moved relative to the workpiece (12); an optical coherence tomograph (24) for generating a measuring beam (26), which can be directed selectively to different measuring positions (28); and a control unit (64) configured to: set a spot pattern (20) that defines at least two different impact points (22); Determining a coordinate system (30), the coordinate system (30) being stationary with respect to the spot pattern (20); and setting a measuring position (28) with respect to the Coordinate system (30) during multispot processing.

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